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Syo Yoshida, Ryohei Misumi, and Takeshi Maesaka


Cumulonimbus clouds, which cause local heavy rainfall and urban floods, can develop within 20 min after being detected by operational centimeter-wavelength (X-, C-, or S-band) weather radars. To detect such clouds with greater lead times, Ka-band radars at a wavelength of 8.6 mm together with operational X-band radars were used in this study. The vertically averaged radar reflectivity (VAR) of convective echoes detected by the Ka-band and X-band radars were defined as mesoscale cloud echoes (MCEs) and mesoscale precipitation echoes (MPEs), respectively. The time series of each echo was analyzed by an echo tracking algorithm. On average, MCEs that developed into MPEs (denoted as developed MCEs) were detected 17 min earlier than the MPEs and 33 min earlier than the peak time of the area-averaged VAR (VARa) for MPEs. Some MCEs dissipated without developing into MPEs (denoted as non-developed MCEs). There were statistically significant differences between the developed and non-developed MCEs in terms of the maximum VARa values, maximum MCEs areas, and increase amounts of the VARa values and MCE areas for the first 6–12 min after their detection. Among these indicators, the maximum VARa for the first 9 min showed the most significant differences. Therefore, an algorithm for predicting MCE development using this indicator is discussed.

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Shingo Shimizu, Hiroshi Uyeda, Qoosaku Moteki, Takeshi Maesaka, Yoshimasa Takaya, Kenji Akaeda, Teruyuki Kato, and Masanori Yoshizaki


The structure and formation mechanism of a supercell-like storm in a moist environment below a melting layer were investigated using dual-Doppler radar analysis and a cloud-resolving storm simulator (CReSS). The supercell-like storm developed over the Kanto Plain, Japan, on 24 May 2000. The environment of the supercell-like storm possessed large convective available potential energy (1000 J kg−1), strong vertical wind shear (4.2 × 10−3 s−1 between the surface and 5 km above sea level), and a moist layer (the relative humidity was 60%–90% below a melting layer at 3 km in height). The dual-Doppler radar analysis with a variational method revealed that the supercell-like storm had similar structures to those of a typical supercell in a dry environment below a melting layer, such as that in the Great Plains in the United States. The structures included a hook echo, an overhanging echo structure, and a strong updraft with strong vertical vorticity. However, some of the characteristics of the supercell-like storm differed from those of a typical supercell. For example, a weak downdraft, a weak outflow, a weak inflow, and a short time maintenance of a single cyclonically rotating updraft (about 30 min) were noted. Dual-Doppler radar analysis revealed that the convergence between the weak outflow and the weak inflow kept its location just under the updraft for about 30 min; in other words, the strength of the outflow balanced the strength of the inflow. The observed features were simulated well using CReSS, and the thermodynamical features of the formation mechanism were revealed. The weak downdraft with a small evaporative cooling rate was simulated in a moist layer below the melting layer at 3 km in height. The small evaporation cooling was a major cause of the weak downdraft and the weak outflow. Because the outflow was weak and did not cut off the initial updraft, the weak inflow was able to keep supplying warm air to the initial updraft for about 30 min. Therefore, the present supercell-like storm could form as a result of the balance of the strengths of the weak inflow and the weak outflow in a moist environment.

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Tsuyoshi Nakatani, Ryohei Misumi, Yoshinori Shoji, Kazuo Saito, Hiromu Seko, Naoko Seino, Shin-ichi Suzuki, Yukari Shusse, Takeshi Maesaka, and Hirofumi Sugawara
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